## Fuel Cell Calculations

Example 10-1 Fuel Flow Rate for 1 Ampere of Current (Conversion Factor Derivation) What hydrogen flow rate is required to generate 1.0 ampere of current in a fuel cell (This exercise will generate a very useful conversion factor for subsequent calculations.) For every molecule of hydrogen (H2) that reacts within a fuel cell, two electrons are liberated at the fuel cell anode. This is most easily seen in the PAFC and PEFC because of the simplicity of the anode (fuel) reaction, although the rule...

## Fuel Processing Calculations

Example 10-8 Methane Reforming - Determine the Reformate Composition Given a steam reformer operating at 1400 F, 3 atmospheres, pure methane feed stock, and a steam to carbon ratio of 2 (2 lb mol H2O to 1 lb mol CH4), (a). List the relevant reactions, (b) Determine the equilibrium concentration assuming the effluent exits the reactor in equilibrium at 1400 F (c) Determine the heats of reaction for the reformer's reactions. (d) Determine the reformer's heat requirement assuming the feed stocks...

## Fuel Cell Performance

The purpose of this section is to provide the framework to understand the chemical and thermodynamic operation of fuel cells, i.e., how operating conditions affect the performance of fuel cells. The impact of variables, such as temperature, pressure, and gas constituents, on fuel cell performance needs to be assessed to predict how the cells interact with the power plant system supporting it. Understanding the impact of these variables allows system analysis studies to engineer a specific fuel...

## Intermediate Temperature Solid Oxide Fuel Cell

The intermediate temperature range for a Solid Oxide Fuel Cell (SOFC) can be arbitrarily defined as 550* C to 800* C. Reducing the operating temperature of the SOFC stack is one of the significant directions being pursued to reduce the cost of SOFC stacks and balance of plant. There are both beneficial effects of reducing stack temperature and detrimental effects. In-the-balance, in most situations, the net effect is beneficial particularly in regard to cost. The most significant obstacle is...

## Hybrid Electric Vehicles HEV

Hybrid Electric Vehicles (HEVs) typically combine the conventional internal combustion engine of the automobile with an energy storage device, such as a battery. However, there are many different arrangements for the HEV. The key components to an HEV are the energy storage system (batteries, ultracapacitors, and flywheels), the power unit (spark ignition engines, compression ignition direct injection engines, gas turbines and fuel cells) and the vehicle propulsion system (electric motor). The...

## Heat and Fuel Recovery Cycles

Simple representations of three fuel cell based heat and fuel recovery cycles are shown in Figures 9-12, 9-13, and 9-16. Regenerative Brayton Cycle The regenerative Brayton cycle, Figure 9-13, shows a gas turbine compressor for the air flow to the cell. The flow then passes through a countercurrent, recuperative heat exchanger to recover heat from the combustion product gases leaving the gas turbine. The air and the fuel streams then pass into the cathode and anode compartments of the fuel cell...

## Power Conditioners and Grid Interconnection

Power conditioning for a fuel cell power plant used to supply DC rated equipment includes current and voltage controls. Power conditioning for a fuel cell power plant used to supply AC rated equipment includes DC to AC inversion and current, voltage and frequency control, stepping the voltage up or down through a transformer depending on final equipment utilization voltage, and maintaining harmonics output to an acceptable level. In addition, transient response of the power conditioning...

## Vehicle Motive Power

Since the late 1980s, there has been a strong push to develop fuel cells for use in light-duty and heavy-duty vehicle propulsion. A major drive for this development is the need for clean, efficient cars, trucks, and buses that can operate on conventional fuels gasoline, diesel , as well as renewable and alternative fuels hydrogen, methanol, ethanol, natural gas, and other hydrocarbons . With hydrogen as the on-board fuel, such vehicles would be zero emission vehicles. With on-board fuels other...

## Stationary Electric Power

One of the characteristics of fuel cell systems is that their efficiency is nearly unaffected by size. This means that small, relatively high efficient power plants can be developed, thus avoiding the higher cost exposure associated with large plant development. As a result, initial stationary plant development has been focused on several hundred kW to low MW capacity plants. Smaller plants several hundred kW to 1 to 2 MW can be sited at the user's facility and are suited for cogeneration...

## Effect of Impurities

The concentrations of impurities entering the PAFC are very low relative to diluents and reactant gases, but their impact on performance is significant. Some impurities e.g., sulfur compounds originate from fuel gas entering the fuel processor and are carried into the fuel cell with the reformed fuel, whereas others e.g., CO are produced in the fuel processor. Carbon Monoxide The presence of CO in a H2-rich fuel has a significant effect on anode performance because CO affects Pt electrodes...

## Natural Gas Fueled Pressurized SOFC System

This natural gas fuel cell power system is based on a pressurized TSOFC combined with a combustion turbine developed by Siemens Westinghouse 52 . Most TSOFC power plant concepts developed to date have been based on atmospheric operation. However, as shown in 53. The referenced Siemens Westinghouse publication presented the cycle concept and overall performance values. Neither specific stream information nor assumptions were presented. The stream data and assumptions presented here were...

## Codes Standards

A summary of existing and pending fuel cell related codes and standards is presented in Table 11-2. More detailed descriptions are provided subsequently based on their specific area of Table 11-2 Summary of Related Codes and Standards Table 11-2 Summary of Related Codes and Standards Performance Test Code - Will provide test procedures, methods and definitions for the performance characterization of fuel cell power systems. Standards coordinating committee - fuel cells, photo-voltaics,...

## Electrochemical Society Extended Abstract Fall Meeting 1976 Las Vegas

Soc., 129, 942, 1982. 2. H.C. Maru, L.G. Marianowski, Extended Abstracts, Abstract 31, Fall Meeting of the Electrochemical Society, October 17-22, 1976, Las Vegas, NV, Pg. 82, 1976. 3. J. Mitteldorf, G. Wilemski, J. Electrochem. Soc., 131, 1784, 1984. 4. H.C. Maru, A. Pigeaud, R. Chamberlin, G. Wilemski, in Proceedings of the Symposium on Electrochemical Modeling of Battery, Fuel Cell, and Photoenergy Conversion Systems, edited by J.R. Selman and H.C. Maru, The...

## References

Foulkes, Fuel Cell Handbook, Van Nostrand Reinhold, New York, NY, 1989. 2. Report of the DOE Advanced Fuel-Cell Commercialization Working Group, Edited by S.S. Penner, DOE ER 0643, prepared by the DOE Advanced Fuel Cell Working Group AFC2WG or the United States Department of Energy under Contract No. DEFG03-93ER30213, March 1995. 3. K. Kordesch, J. Gsellmann, S. Jahangir, M. Schautz, in Proceedings of the Symposium on Porous Electrodes Theory and Practice, Edited by H.C....

## Natural Gas Processing

The major constituents of pipeline gas are methane, ethane, propane, CO2, and, in some cases, N2. Sulfur containing odorants mercaptans, disulfides, or commercial odorants are added for leak detection. Because neither fuel cells nor commercial reformer catalysts are sulfur tolerant, the sulfur must be removed. This is usually accomplished with a zinc oxide sulfur polisher and the possible use of a hydrodesulfurizer, if required. The zinc oxide polisher is able to remove the mercaptans and...

## Effect of Pressure

The dependence of reversible cell potential on pressure is evident from the Nernst equation. For a change in pressure from P1 to P2, the change in reversible potential AVp is given by where the subscripts a and c refer to the anode and cathode, respectively. In an MCFC with the anode and cathode compartments at the same pressure i.e., P1 P1,a P1,c and P2 P2,a P2,c P2 I P2 AVp mV 20 ln I 46 log Thus, a tenfold increase in cell pressure corresponds to an increase of 46 mV in the reversible cell...

## Effect of Reactant Gas Composition and Utilization

The voltage of MCFCs varies with the composition of the reactant gases. The effect of reactant gas partial pressure, however, is somewhat difficult to analyze. One reason involves the water gas shift reaction at the anode due to the presence of CO. The other reason is related to the consumption of both CO2 and O2 at the cathode. Data 55,64,65,66 show that increasing the reactant gas utilization generally decreases cell performance. As reactant gases are consumed in an operating cell, the cell...

## Uf H

Where H2,in and H2,out are the mass flow rates of H2 at the inlet and outlet of the fuel cell, respectively. However, hydrogen can be consumed by various other pathways, such as by chemical reaction i.e., with O2 and cell components and loss via leakage out of the cell. These pathways increase the apparent utilization of hydrogen without contributing to the electrical energy produced by the fuel cell. A similar type of calculation is used to determine the oxidant utilization. For the cathode in...

## SOFC System Cost Structure

The main difference in SOFC stack cost structure as compared to PEFC cost relates to the simpler system configuration of the SOFC-based system. This is mainly due to the fact that SOFC stacks do not contain the type of high-cost precious metals that PEFCs contain. This is off-set in part by the relatively complex manufacturing process required for the manufacture of the SOFC electrode electrolyte plates and by the somewhat lower power density in SOFC systems. Low temperature operation enabled...

## Coal Fueled SOFC System Vision

The coal fueled solid oxide fuel cell power system presented here is based on work performed for the Department of Energy's Vision 21 Program 57 to develop of high efficiency, low emission, fuel flexible including coal processes. This cycle is a coal-fueled version of the Siemens Westinghouse TSOFC cycle presented in Section 9.3.5 consists of a Destec gasifier, cascaded SOFCs at two pressure levels, an integrated reheat gas turbine, and a reheat steam turbine bottoming cycle. The high-pressure...

## Fuel Cells Doe Metc 86 0241

Am. Ceram. Soc., p. 76 3 563-88, 1993. 2. Courtesy of Siemens Westinghouse. 3. T.H. Etsell, S.N. Flengas, J. Electrochem. Soc, p. 118, 1890 1971 . 4. A.O. Isenberg, in Proceedings of the Symposium on Electrode Materials and Processes for Energy Conversion and Storage, edited by J.D.E. Mclntyre, S. Srinivasan and F.G. Will, The Electrochemical Society, Inc., Pennington, NJ, 1977, p. 682. 5. A.O. Isenberg, in Proceedings of the Symposium on Electrode Materials...

## Cell Configuration Options

As with the other cell types, it is necessary to stack SOFCs to increase the voltage and power being produced. Because there are no liquid components, the SOFC can be cast into flexible shapes Figure 8-1 . In the early 1960s, experimental SOFCs with a planar geometry were evaluated, but this geometry presented a problem for building cell stacks because of difficulties with fabricating large flat, thin cells and obtaining adequate gas seals. A tubular configuration i.e., cylindrical design...

## Equilibrium Constants

Figure 11-1 presents the temperature dependence of the equilibrium constants for the water gas shift reaction, the carbon deposition Boudouard reaction reaction, 600 700 800 900 1000 1100 1200 1300 Temperature K Figure 11-1 Equilibrium Constants Partial Pressures in MPa for a Water Gas Shift, b Methane Formation, c Carbon Deposition Boudouard Reaction , and d Methane Decomposition J.R. Rostrup-Nielsen, in Catalysis Science and Technology, Edited by J.R. Anderson and M. Boudart, Springer-Verlag,...

## Efficiency Calculations

Example 10-11 LHV, HHV Efficiency and Heat Rate Calculations Given a 2.0 MWAC fuel cell cycle operating on 700 lb hr of methane, what is a the HHV65 thermal input of the methane gas, b the LHV thermal input, c the HHV electric efficiency, d the LHV electric efficiency, and e the HHV Heat Rate Assume the higher and lower heating value of methane as 23,881 and 21,526 Btu lb respectively. a The HHV thermal input of the methane gas is HHV Thermal Input 700lb h CH4 2W Btu, HHVIfiM l 16.716 MMBtu h,...

## Figure Overview of subsystems and components for SOFC and PEM systems

Figure 1-14 shows a simplified layout for an SOFC-based APU. The air for reformer operation and cathode requirements is compressed in a single compressor and then split between the unit operations. The external water supply shown in figure 1-14 will most likely not be needed the anode recycle stream provides water. Unreacted anode tail gas is recuperated in a tail gas burner. Additional energy is available in a SOFC system from enthalpy recovery from tail gas effluent streams that are typically...

## Alkaline Fuel Cell

The Alkaline Fuel Cell AFC was one of the first modern fuel cells to be developed, beginning in 1960. The application at that time was to provide on-board electric power for the Apollo space vehicle. Desirable attributes of the AFC include its excellent performance on hydrogen H2 and oxygen O2 compared to other candidate fuel cells due to its active O2 electrode kinetics and its flexibility to use a wide range of electrocatalysts, an attribute which provides development flexibility. The AFC...

## Natural Gas Fueled Internally Reformed MCFC System

Fuel Cell Energy expects to have its initial market entry MCFC power systems available in the year 2001, with mature megawatt class units projected to be available in 2004. These units will be produced in various sizes. Preliminary cycle information was received from FCE for a nominal 3 MW power plant. This cycle is presented in Figure 9-9 and is described below. Figure 9-9 Natural Gas Fueled MCFC Power System Figure 9-9 Natural Gas Fueled MCFC Power System Natural gas is cleaned of its sulfur...

## Gibbs Free Energy and Ideal Performance

The maximum electrical work Wel obtainable in a fuel cell operating at constant temperature and pressure is given by the change in Gibbs free energy AG 12 of the electrochemical reaction, where n is the number of electrons participating in the reaction, F is Faraday's constant 96,487 coulombs g-mole electron , and E is the ideal potential of the cell. If we consider the case of reactants and products being in the standard state, then 10. Constraints can limit the degree of part load operation...

## Natural Gas Fueled Multi Stage Solid State Power Plant System

The Fuel Cell system presented below is based on an innovative solid state fuel cell system developed by U.S.DOE 54 . Conventional fuel cell networks, in order to effectively use the supplied fuel, often employ fuel cell modules operating in series to achieve high fuel utilization55 or combust the remaining fuel for possible thermal integration such as cogeneration steam or a steam bottoming cycle. Both of these conventional approaches utilize fuel cell modules at a single state-of-the-art...

## Natural Gas Fueled PEFC System

A natural gas PEFC power plant configuration is shown in Figure 9-7 and is a slight simplification of a cycle published in 1997 by a Ballard Researcher 48 . In light of the PEFC sensitivity to CO, CO2 and methane, the fuel processing represents a significant portion of the cycle. Natural gas fuel enters a fuel compressor and a fuel cleanup device. The reference document does not describe the cleanup device, but it is assumed to be a sulfur polisher to prevent poisoning of the fuel cell...

## Polarization Activation Tafel and Concentration

To determine actual cell performance, three losses must be deducted from the Nernst potential activation polarization, ohmic polarization, and concentration polarization. Definition of the ohmic polarization is simply the product of cell current and cell resistance. Both activation polarization and concentration polarization required additional description for basic understanding. Activation Polarization It is customary to express the voltage drop due to activation polarization by a...